Process of recovering nitrogen from residual ammonia oxidation gases



Patented Mar. 18, 1924.

'cucouo FAUSEB, or 'novnflj'rranx. I success or momma macaw rnou nnsmuenamronm oxrnarron cssnsi To all whom it may cement:

Be it known that I,- Gmcomo. FAUSER,

siding at Novara, Italy, have invented new and useful Improvements in Processes of Recovering Nitro n. from Residual Am-- monia Oxidation ases, of which the follow: ing is a specification.

.is known that by the oxidation of am-- monia, nitric acid can be obtained. The fundamental reactions can be represented by the following equations:

tains 23 per cent oxygen, the ratio between air and ammonia will be in weight equivalent to 112 100 w 14 (about). To the neccessaryoxy for oxidizing the ammonia is to ad ed that necessary to the successive reoxidation ofNO to NO because, as shown by the above equations the reaction permits in each cycle the transformation into HNO only of two thirds of the N 0 present while the remainder returns to the form of NO which is to be reoxidized. I calculate easily that. such supplemental oxygen is about 0.17 kg. per kg. of N0 and as 1 kg. of ammonia by oxidlzation gives 2.7 kg. of N0 the ratio between the weight of oxygen and the weight of ammonia used will be of O.17 2.7=0.459 and therefore the weight of the corresponding air will be:

2 (about) used, and it has been sug by some one even resortin Appllcation-flled April 11, 1922. Serial Ila-551,730.

' to introduce still acertain quantity of supplemental air in the oxidation towers. This method however has the drawback of fur- .therdiluting the oxides and consequently of -mak1ng-the1r absorption more diflicult and slower; therefore it is not recommendable.

It has been suggested that for absorbing 99% of the oxides of nitrogen which are in the gases, it .should be necessary to repeat the c ole-at least 9 times in succession but 'as t e concentration of the oxides of nitrogen d1minishes,.the regeneration of N 0 becomes increasingly diflicult, so that to absorption towers with alkaline solutions instead of Water, the recovery of the oxides of nitrogen can never be complete. To sum up from the above observations, the gases leaving the last absorption device,

always contain traces of oxides of nitrogen but these gases are chiefly composed of nitrogen; the oxygen is contained in variable proportions from about 4 to 5% according to the initial composition of the air-ammonia mixture.

I propose to utilize such gases for the production of pure nitrogen, which can be used for producing synthetic ammonia, calcium cyanamide and for other ur oses.

In order to diminish t e al contents of oxygen it is convenient to limit the amount of air as much as is consistent with securing a good yield of nitric acid. The theoretical ratio being, as already calculated, 16 kg. per kg. of ammonia.

For eliminating the oxygen a sufiicient small percentage of hydrogen is added to the residual gases from the oxidation of ammonia, thence they are brought into contact with a (platinum coil, whlch ismain' tained incan escent by the electric current. This causes the combustion of hydrogen with oxy en forming water vapor, which is condense and separated. Traces of the O are decomposed if the temperature of the catalyst is high enough, into oxygen and nitro en. However it 1s well to remark that 1n contrast to the oxygenated compounds of carbon,'oxides of nitrogen have no destructive action on the catalyzers used for the synthesis of ammonia. The small amount of oxidesof nitrogen can be more advantageously recovered by passing the mixture of gas with hydrogen over a suitable ,catalyzer, which may be platinized asbestos, at a lower tem erature. The following reaction takes p ace:

NO+3H,=NH,+H,O.

In this way nearly all the nitrogen contained in the gases is recovered in the form of ammonia. Also the oxygen present is eliminated by passing over the catalyzer to form H O (water vapor) and the condensation of this removes the N11,. There remains then the pure nitrogen, winch 18 thus produced at a very low price.

By increasing opportunely the proport on of hydrogen we can directly obtain the mixture N +3H required bythe synthesis of ammonia.

The advantage of resorting to residual ases of the oxidation of ammonia for proucing nitrogen is evident if we consider the small amount of oxygen contained therein in comparison with the content atmospheric air. In fact it results that for producing 1 kg. of nitrogen by burning the oxygen of the air it is necessary to consume about 430 liters of hydrogen, and considerin that 6 kw. hours are required for the pro notion of lm of H by the electrolysis of the water,

menace of energy consumed only about kw. hour 0.40.

N ow what I claim is:

In the production of free nitrogen from the exit gases from the oxidation of ammonia and subsequent oxidation and absorption of nitrogen oxide, which exit gases contam oxygen and nitrogen and a proportion of oxygen which is only a minor fraction of the content of oxygen in air, and which exit gases may also contain a much smaller percentage of an oxide of nitrogen, which comprises adding hydrogen in amount at least chemically equivalent to the. present and passing the gas mixture in contact with a catalyzer at a temperature at which free oxygen and hydrogen combine to form water, then separating the water. GIACOMG FAUSER.

oxygen 

